Electric motors and related systems for deployment in a downhole well environment

ABSTRACT

A method can include providing a motor that includes a housing, axially aligned stationary electromagnets disposed in the housing, an aperture defined by the axially aligned stationary electromagnets, movable axially aligned permanent magnets disposed in the aperture and a connector shaft connected at an end of the movable axially aligned permanent magnets; disposing the motor and a rod pump in a well; controlling operation of the motor to linearly reciprocate the axially aligned movable permanent magnets and the connector shaft; pumping fluid from the well via the rod pump responsive to the linear reciprocation of the axially aligned movable permanent magnets and the connector shaft; and substantially blocking the pumped fluid from flowing through the aperture defined by the axially aligned stationary electromagnets of the motor. Various other apparatuses, systems, methods, etc., are also disclosed.

RELATED APPLICATION

This application is a continuation of a co-pending U.S. patentapplication having Ser. No. 12/572,548, filed 2 Oct. 2009, now U.S. Pat.No. 8,587,163, issued 19 Nov. 2013, which are incorporated by referenceherein.

FIELD

The present application relates to the oil field industry and morespecifically to motors that supply output to an operable productiondevice in a well, such as for example a pump, sleeve, valve or othermechanical device. The disclosures provided herein can be particularlyuseful in small-bore applications.

BACKGROUND

Artificial lift in wells can be achieved by the use of downhole electricmotors that convert rotational motion to linear motion, or by the use ofsurface-bound rod pumps. Electric motors typically employ magneticforces to create rotational motion, which is then converted to linearmotion in order to provide output to an operable production device, suchas a pump or other mechanical device. The conversion of rotationalmotion to linear motion involves failure-prone mechanisms and complexmoving parts, which disadvantageously introduce efficiency and/orreliability losses to the system. This rotational-to-linear conversionis also impractical in special small-bore applications, where spaceconstraints limit the size of the motor and therefore its outputcapabilities. Current non-rotational artificial lift methods, such asrod pumps, disadvantageously require surface motors and extensiveshafting to couple a source of power to a downhole linear pump. Thesemethods are not a viable option in areas where above-ground space is ata premium.

SUMMARY

The present disclosure provides improved electric motor configurationsfor deployment in a downhole well environment. The unique configurationsemploy linear reciprocating movement of a series of aligned magnetsincluding one or more movable magnets in combination with one or morestationary magnets. This advantageously provides raw linear output,while taking up relatively little annular space in the well. Thistechnology is thus especially suitable for use in small wellbores whereother artificial lift methods are difficult to implement.

In one example, two groups of magnets are interdigitated and haveopposing faces. Reversing the polarity of one of the groups of magnetscauses reciprocation of the movable magnet(s) and provides linear outputto the noted production device. In another example, the groups ofmagnets are aligned adjacent each other and the movable magnet(s) is/aremovable axially between a first position proximate the outer end of oneof the stationary magnets and a second position proximate the outer endof another of the stationary magnets. Reversing the polarity of one ofthe groups of magnets causes reciprocation of the movable magnet(s) andprovides the linear output to the production device. The magnets can be,for example, disc-shaped or rod-shaped.

In broader terms, one example of the electric motor includes a housingcontaining a series of magnets. The series includes at least threemagnets, including two outer magnets and an inner magnet disposedbetween the two outer magnets. The two outer magnets have inside faceswith like poles and outside faces with like poles. One of the innermagnet and the two outer magnets is stationary, while the other ismovable. The one of the inner magnet and the two outer magnets that ismovable moves between a first position in which the inner magnet islocated proximate to one of the outer two magnets, and a second positionin which the inner magnet is located proximate to the other of the twoouter magnets. The one of the inner magnet and the two outer magnetsthat is movable is configured for connection to an operable productiondevice. A supply of alternating current is coupled to the series ofmagnets so as to alternate the polarity of one of the inner magnet andthe two outer magnets to thereby cause the one of the inner magnet andthe two outer magnets that is movable to reciprocate between the firstand second positions, and to thereby provide reciprocating linear outputto drive the operable production device.

Another example of the electric motor includes a housing containing aplurality of aligned magnets. The plurality of magnets includes at leasttwo adjacent, axially-aligned stationary magnets having outer endshaving the same polarity and inner ends having the same polarity. Theplurality of magnets also includes at least one movable magnet disposedadjacent to, or more specifically, within the stationary magnets. Themovable magnet is movable axially between a first position proximate theouter end of one of the stationary magnets and a second positionproximate the outer end of the other stationary magnet. The movablemagnet is configured for connection to an operable production device inthe well. A supply of alternating current is coupled to the plurality ofmagnets so as to alternate the polarity of one of the movable andstationary magnets to thereby cause the movable magnet to reciprocatebetween the first and second positions, and to thereby providereciprocating linear output to drive the operable production device.

Downhole well pumping systems for artificial lift are also provided. Thesystems include a production pump disposed in a downhole wellenvironment and an electric motor coupled to the production pump andoperable to provide reciprocating linear output to drive the productionpump. The configuration of the electric motor can be that of either ofthe two examples described above. A controller is configured to controloperation of the electric motor by selectively supplying alternatingcurrent to the electric motor and to thereby provide reciprocatinglinear output to drive the operable production device.

BRIEF DESCRIPTION OF THE DRAWINGS

A best mode is described herein below with reference to the followingdrawing figures.

FIG. 1 depicts a downhole well pumping system according to one exampleof the present disclosure.

FIG. 2 depicts one example of an electric motor according to the presentdisclosure for deployment in a downhole well environment, wherein twoinner magnets that are movable are positioned in a first position.

FIG. 3 depicts the example shown in FIG. 2, wherein the inner magnetsare positioned in a second position.

FIG. 4 depicts another example of an electric motor according to thepresent disclosure, wherein a series of magnets are disc-shaped.

FIG. 5 depicts another example of an electric motor according to thepresent disclosure, wherein a series of magnets are rod-shaped.

FIG. 6 depicts another example of an electric motor according to thepresent disclosure, wherein a movable magnet is moved into a firstposition proximate an outer end of one of two adjacent, axially-alignedstationary magnets.

FIG. 7 depicts the example in FIG. 6 wherein the movable magnet ispositioned in a second position proximate the outer end of the other ofthe two adjacent, axially-aligned stationary magnets.

FIG. 8 depicts the example in FIG. 2 wherein the two inner magnets thatare movable are connected to a spring.

DETAILED DESCRIPTION OF THE DRAWINGS

In the following description, certain terms have been used for brevity,clearness, and understanding. No unnecessary limitations are to beimplied therefrom beyond the requirement of the prior art because suchterms are used for descriptive purposes and are intended to be broadlyconstrued. The different configurations described herein may be usedalone or in combination with other configurations and systems. Variousequivalents, alternatives, and modifications are possible within thescope of the appended claims.

FIG. 1 depicts a well 11 that extends from a surface 14 into anunderground or downhole well environment in a reservoir 12. The well 11can be of any length and in the preferred example is a small-boreapplication. In the example shown, the well 11 has a verticalorientation; however, the well 11 can also or alternately extend at anangle or horizontal to the surface 14.

FIG. 1 also depicts an example of a system 10 according to the presentdisclosure. System 10 includes a controller 16, an electric motor 18,and related operable production device 20. The controller 16 preferablyincludes a memory and a programmable code which can be executed tocontrol operation of the electric motor 18, such as for example tooperate a source of power 17 to selectively supply alternating currentto the electric motor 18 and to thereby provide a reciprocating linearoutput to the operable production device 20, as described further hereinbelow. In the example shown, the controller 16 is located at the surface14 and is communicatively attached to the source of power 17 and to theelectric motor 18 via wired or wireless links 19, 21. This arrangementadvantageously requires a minimal surface footprint. In other examples,the controller 16 could be attached directly to the motor 18 or to, forexample, other related operating equipment. The electric motor 18 iscoupled to the operable production device 20 and is configured toprovide the noted reciprocating linear output to drive the operableproduction device 20. In the example shown, the operable productiondevice 20 is a pump, such as a piston pump or a diaphragm or bag(bellows) pump; however it could comprise any other downhole mechanicaldevice capable of receiving input from the motor 18.

FIG. 2 depicts one example of the electric motor 18 according to thepresent disclosure. In this example, an electric motor 18 a includes ahousing 32 containing a series of magnets 23 aligned along an axialdirection (A). The housing 32 serves as a mechanical support for theseries of magnets 23 and as a path for magnetic flux, as will bedescribed herein below. The series of magnets 23 includes a first groupof magnets (“outer magnets”) 26 a, 26 b, and 26 c and a second group ofmagnets (“inner magnets”) 28 a, 28 b disposed between the first group ofmagnets 26 a-26 c in an interdigitated configuration. The faces of themagnets 26 a, 26 b and 26 c are aligned so as to have poles that are notall oriented the same in the axial direction. Rather, the poles at theopposing faces of the two magnets 26 a, 26 b are both south and thepoles at the respective opposite faces of the magnets 26 a, 26 b areboth north. In the same way, the poles at the opposing faces of the twomagnets 26 b, 26 c are both north and the poles at the respectiveopposite faces of the magnets 26 b, 26 c are both south. The faces ofthe magnets 28 a, 28 b are also aligned so as to have poles that are notoriented the same in the axial direction. The poles at the opposingfaces of the magnets 28 a, 28 b are both north, while the poles at theopposite faces of the magnets 28 a, 28 b are both south. The magnet 28 ais aligned such that it is attracted to one of the opposing faces of thetwo magnets 26 a, 26 b and repelled from the other. The magnet 28 b isaligned such that it is attracted to one of the opposing faces of thetwo magnets 26 b, 26 c and repelled from the other. Preferably themagnets 26 a-26 c and 28 a, 28 b are electromagnets; however, othertypes of magnets may be employed.

In the example shown, the magnets 26 a-26 c are stationary magnets,while the magnets 28 a, 28 b are movable magnets. The outer magnets 26a-26 c are fixed in relation to the housing 32 and thus remainstationary relative to the housing 32. In contrast, the inner magnets 28a, 28 b are movable in the axial direction (A) and movable relative tothe outer magnets 26 a-26 c between first and second positions shown inFIGS. 2 and 3, respectively. It is only necessary that one of the groupsof magnets 28 a, 28 b or 26 a-26 c remain stationary, while the other ismovable between the first and second positions shown in FIGS. 2 and 3,respectively. In other words, the outer magnets 26 a-26 c could bemovable, whereas the inner magnets 28 a, 28 b could remain stationary.It is also possible to construct the motor 18 a with fewer or moremagnets in each group. For example, the housing 32 could contain aseries of magnets including only two outer magnets (e.g. 26 a, 26 b) andan inner magnet (e.g. 28 a) disposed between the two outer magnets,wherein the two outer magnets have opposing faces with like poles andopposite faces with like poles. In this example, either of the twogroups of magnets could be movable and connected to the device 20, withthe other remaining stationary.

In the example shown, the movable magnet 28 a is connected to themovable magnet 28 b by a connector shaft 30 b. Another connector shaft30 a connects the movable magnet 28 a and the movable magnet 28 b to theoperable production device 20 (schematically shown in dashed lines) insuch a manner that movement of the magnets 28 a, 28 b is conveyed to theoperable production device 20. Another connector shaft 30 c is alsoprovided and is optionally removably connected to another series ofmagnets 31 (schematically shown in dashed lines) to increase or decreaseproductive output of the motor 18. In this unique modular design, theamount of linear output provided to the device 20 can be easilyincreased by adding additional series of magnets 31 to the motor 18 a ina stacked formation and easily decreased by subtracting additionalseries of magnets 31 from the formation. The three connector shafts 30a-30 c are separate, but could alternately be replaced with a singleconnector shaft extending through and/or around the various magnets inthe series 23.

FIG. 8 depicts the electric motor 18 a, wherein a spring 34 has beenintroduced into the series 23. The movable magnets 28 a, 28 b areconnected to the spring 34 by the connector shaft 30 c. The spring 34 isaligned such that it shortens and lengthens in the axial direction (A).One end of the spring 34 is connected to the connector shaft 30 c, whilethe other end of the spring 34 is connected to the housing 32. Thehousing 32 has an aperture 33 which allows the connector shaft 30 c tomove through the housing 32. The spring can be used to increase theusable linear output of the motor 18 a by smoothing the quadraticresponse created as the movable magnets move towards or away from thestationary magnets. The spring can also be used to pre-load the seriesof magnets 23 to increase the linear output in one direction, whiledecreasing it in the other direction.

In the example shown, the source of power 17 is connected to thestationary outer magnets 26 a-26 c by a wired link 21, preferably wiredthrough the housing 32, to provide a supply of alternating current tothe magnets 26 a-26 c and to thereby cause the poles of the magnets 26a-26 c to alternate between the orientation in which the opposing facesof 26 a, 26 b have like south poles and the opposing faces of 26 b, 26 chave like north poles (shown in FIG. 2), and the orientation in whichthe opposing faces of 26 a, 26 b have like north poles and the opposingfaces of 26 b, 26 c have like south poles (shown in FIG. 3). Alternatingthe polarity of the magnets 26 a, 26 b causes the magnet 28 a toreciprocate back and forth between the noted first and second positionsshown in FIGS. 2 and 3 respectively, while alternating the polarity ofthe magnets 26 b, 26 c causes the magnet 28 b to reciprocate back andforth between the noted first and second positions. More specifically,FIG. 2 depicts the magnet 28 a moved into a first position wherein themagnet 28 a has a south-north pole orientation in the axial direction(A). The north pole of the magnet 28 a is attracted to the south pole ofthe magnet 26 b. When the current is alternated and the pole orientationof the magnets 26 a, 26 b is switched so that the opposing faces areboth north poles, the north pole of the magnet 28 a repels from thenorth pole of the magnet 26 b, while the south pole of the magnet 28 aattracts to the north pole of the magnet 26 a. Thus, the magnet 28 amoves from the first position shown in FIG. 2 to the second positionshown in FIG. 3. When the current is alternated once again and theopposing faces of the magnets 26 a, 26 b are again south poles, themagnet 28 a will again move to the first position shown in FIG. 2, whereits north pole will be attracted to the south pole of the magnet 26 b,while its south pole will be repelled from the south pole of the magnet26 a. The same repulsion and attraction occurs between magnets 26 b, 26c, and 28 b. In FIG. 2, the south pole of the magnet 28 b is attractedto the north pole of the magnet 26 c. When the current is alternated andthe pole orientation of the magnets 26 b, 26 c is switched so that theopposing faces are both south poles, the south pole of the magnet 28 brepels from the south pole of the magnet 26 c, while the north pole ofthe magnet 28 b attracts to the south pole of the magnet 26 b. Thus, themagnet 28 b moves from the first position shown in FIG. 2 to the secondposition shown in FIG. 3. When the current is alternated once again andthe opposing faces of the outer magnets 26 b, 26 c are again northpoles, the magnet 28 b will again move to the first position shown inFIG. 2, where its south pole will be attracted to the north pole of themagnet 26 c, while its north pole will be repelled from the north poleof the magnet 26 b.

Providing alternating current to alternate the polarity of the outermagnets 26 a-26 c thereby causes the inner magnets 28 a, 28 b toreciprocate back and forth between the noted first position (FIG. 1) andthe noted second position (FIG. 2) and in turn to provide linear outputto the production device 20.

In another example, the source of power 17 could be connected to themovable magnets 28 a, 28 b to alternate their polarity but not thepolarity of the stationary magnets 26 a-26 c, and to thereby cause thesame reciprocation of the magnets 28 a, 28 b described above. It is tobe understood that the three magnets 26 a-26 c could be movable, whilethe magnets 28 a, 28 b could be stationary. The polarity of either themagnets 28 a, 28 b or the magnets 26 a-26 c could be alternated in thisconfiguration as well to provide reciprocating linear output to theoperable production device 20.

It is also to be understood that the configuration in FIGS. 2 and 3 isshown as an example only, and that the same reciprocating linear motioncould be created by any combination of at least three magnets: two outermagnets and one inner magnet disposed between the outer magnets, one ofthe inner magnet and the two outer magnets being stationary and theother being movable between the first and second positions. Thisdisclosure therefore also contemplates combinations of four magnets,five magnets, six magnets, and so on.

The electric motor 18 a may have various geometries, examples of whichare shown in FIGS. 4 and 5. FIG. 4 shows a variation of the electricmotor 18 a, which uses disc-shaped outer magnets 38 and disc shapedinner magnets 40. FIG. 5 shows another variation of the electric motor18 a, which uses rod-shaped outer magnets 42 and rod-shaped innermagnets 44. Both the disc-shaped magnets 40 and the rod-shaped magnets44 are capable of moving between the first and second positions as shownin FIGS. 2 and 3, respectively. The geometry of the magnets can bevaried as shown in FIGS. 4 and 5 for different applications. Forexample, the rod-shaped magnets 42, 44 are particularly useful insmall-bore applications due to their small diameter.

FIG. 6 depicts another example of the electric motor 18 according to thepresent disclosure. Specifically, an electric motor 18 b includes ahousing 52 containing a plurality of aligned magnets 53 which includesat least two adjacent, stationary magnets 48 and at least one movablemagnet 50 disposed adjacent to the stationary magnets 48 a, 48 b. Thestationary magnets 48 a, 48 b are coupled to the housing 52 and arecoils having outer ends with the same polarity and inner ends with thesame polarity; in the example shown in FIG. 6, the outer ends ofstationary magnets 48 a, 48 b are south poles, while the inner ends ofstationary magnets 48 a, 48 b are north poles. The movable magnet 50 isdisposed adjacent to the stationary magnets 48 a, 48 b. In the exampleshown, the movable magnet 50 is disposed in a through-going aperture 54,defined by the stationary magnets 48 a, 48 b. The movable magnet 50 isconnected to a connector shaft 60 a, 60 b on either end. Connector shaft60 a connects the movable magnet 50 to the operable production device 20in such a manner that movement of the movable magnet 50 is conveyed tothe operable production device 20 (schematically shown in dashed lines).The other connector shaft 60 b is optionally removably connected toanother movable magnet 51 (schematically shown in dashed lines) toincrease or decrease reciprocating linear output of the motor 18 b. Inthis unique modular design, the amount of linear output provided to thedevice 20 can be easily increased by adding additional pluralities ofaligned magnets 53 to the motor 18 b in an axially stacked formation andalso can be easily decreased by subtracting pluralities of magnets 53from the formation. The two connector shafts 60 a, 60 b are separate,but could alternately be replaced with a single shaft extending throughand/or around the movable magnet 50. Preferably the movable magnet 50 isa permanent magnet, while the stationary magnets 48 a, 48 b areelectromagnets; however, other combinations of permanent andelectromagnets may be employed.

The movable magnet 50 and connector shafts 60 a, 60 b are configuredsuch that they substantially block any fluid from flowing through thethrough-going aperture 54. This provides an advantage over the priorart, in which fluid can come into direct contact with the magnets in thehousing and the magnets connected to the shaft. Fluids pumped from wellsoften contain small metallic pieces that stick to permanent magnets inthe motor, and eventually clog the motor. By preventing fluid fromflowing through the through-going aperture 54, this will not occur.

In the example shown, the source of power 17 is connected to thestationary magnets 48 a, 48 b by a wired link 21 to provide a supply ofalternating current to the magnets 48 a, 48 b and to thereby cause thepoles of the magnets 48 a, 48 b to alternate between the orientation inwhich the inner ends of the stationary magnets 48 a, 48 b are northpoles (shown in FIG. 6) and the orientation in which the inner ends ofthe stationary magnets 48 a, 48 b are south poles (shown in FIG. 7).Alternating the north-south orientation of the magnets 48 a, 48 b causesthe movable magnet 50 to reciprocate back and forth between the notedfirst and second positions shown in FIGS. 6 and 7, respectively.Specifically, FIG. 6 depicts the movable magnet 50 in a first positionwherein the movable magnet 50 has a north-south pole orientation. Thesouth pole of the movable magnet 50 is attracted toward the south poleof the stationary magnet 48 b such that, if it were allowed to continuemoving, the south poles of the movable magnet 50 and the stationarymagnet 48 b would be aligned, and the net magnetic force on eithermagnet 50 or 48 b would be zero. However, a physical stop 62 or aposition sensor (not shown) prevents the movable magnet 50 fromcompletely aligning its poles with those of the stationary magnet 48 b.When the current is alternated and the pole orientation of thestationary magnets 48 a, 48 b is changed such that the inner ends of thestationary magnets 48 a, 48 b are both south poles (shown in FIG. 7),the movable magnet 50 attempts to align its north and south poles withthe north and south poles of the stationary magnet 48 a so as to cancelout the net force on either magnet 50 or 48 a. Once again however, thisis prevented by a physical stop 62 or a position sensor (not shown).When the current is again alternated to create the pole orientationshown in FIG. 6, the movable magnet 50 again attempts to align with thestationary magnet 48 b. Thus the movable magnet 50 reciprocates back andforth between the noted first position (FIG. 6) and the noted secondposition (FIG. 7).

In another example, the source of power 17 is connected to the movablemagnet 50 by a wired link 21 to alternate the polarity of the movablemagnet 50 and thereby cause the same reciprocation of the movable magnet50 as described above. However, this is not preferable because providingpower to the movable magnet 50 would require that the wired link 21reciprocate along with the movable magnet 50. Over time, this causes thewired link 21 to wear out, necessitating repair of the electric motor18. Therefore, it is preferable that the movable magnet 50 be apermanent magnet, which does not require a wired link 21 to supply itwith power.

1. A method comprising: providing a controller; providing a rod pump;providing a motor that comprises a housing, axially aligned stationaryelectromagnets disposed in the housing, an aperture defined by theaxially aligned stationary electromagnets, movable axially alignedpermanent magnets disposed in the aperture and a connector shaftconnected at an end of the movable axially aligned permanent magnets;coupling the motor to the rod pump via the connector shaft; disposingthe motor and the rod pump in a well; controlling operation of the motorby selectively supplying alternating current to the axially alignedstationary electromagnets via a power source controlled by thecontroller to linearly reciprocate the axially aligned movable permanentmagnets and the connector shaft; pumping fluid from the well via the rodpump responsive to the linear reciprocation of the axially alignedmovable permanent magnets and the connector shaft; and substantiallyblocking the pumped fluid from flowing through the aperture defined bythe axially aligned stationary electromagnets of the motor.
 2. Themethod of claim 1 comprising providing a position sensor and sensingposition of the axially aligned movable permanent magnets.
 3. The methodof claim 1 further comprising providing another connector shaft at theother end of the axially aligned permanent magnets and connectinganother moveable permanent magnet to the axially aligned permanentmagnets via the other connector shaft.
 4. The method of claim 1 whereinthe well extends from a surface into a well environment and wherein thedisposing the motor and the rod pump in the well comprises disposing themotor and the rod pump horizontally with respect to the surface.
 5. Themethod of claim 1 wherein the controller comprises a memory andprogrammable code wherein the programmable code is executable forcontrolling operation of the motor.
 6. The method of claim 1 wherein thecontroller is provided at a surface and is communicatively attached to asource of power via a wired link.
 7. The method of claim 1 wherein thecontroller is provided at a surface and is communicatively attached to asource of power via a wireless link.
 8. The method of claim 1 whereinthe controller is attached directly to the motor.
 9. The method of claim1 wherein the connector shaft comprises an annular component forsubstantially blocking the pumped fluid from flowing through theaperture defined by the axially aligned stationary electromagnets of themotor.
 10. The method of claim 1 wherein the substantially blocking thepumped fluid from flowing through the aperture defined by the axiallyaligned stationary electromagnets of the motor prevents clogging of theaxially aligned permanent magnets disposed in the aperture defined bythe axially aligned stationary electromagnets of the motor.
 11. Themethod of claim 1 wherein the pumped fluid comprises a fluid from areservoir.
 12. A method comprising: providing a controller; providing arod pump; providing a motor that comprises a housing, axially alignedstationary electromagnets disposed in the housing, an aperture definedby the axially aligned stationary electromagnets, movable axiallyaligned permanent magnets disposed in the aperture and a connector shaftconnected at an end of the movable axially aligned permanent magnets;coupling the motor to the rod pump via the connector shaft; disposingthe motor and the rod pump in a well; controlling operation of the motorby selectively supplying alternating current to the axially alignedstationary electromagnets via a power source controlled by thecontroller to linearly reciprocate the axially aligned movable permanentmagnets and the connector shaft; pumping fluid from the well via the rodpump responsive to the linear reciprocation of the axially alignedmovable permanent magnets and the connector shaft; and preventingclogging of the axially aligned permanent magnets disposed in theaperture defined by the axially aligned stationary electromagnets of themotor by substantially blocking the pumped fluid from flowing throughthe aperture defined by the axially aligned stationary electromagnets ofthe motor.
 13. The method of claim 12 wherein the pumped fluid comprisesmetallic pieces.
 14. The method of claim 13 wherein the metallic piecesare attracted to a magnet.
 15. The method of claim 12 wherein the pumpedfluid comprises a fluid from a reservoir.